Compute Paths in Parallel

[TheDeafCreeper]

The goal of this PR is to resolve #32.

The tasks that need to be done for this are (as listed in the issue):

• [x] Adding suitable Future return values from a path trial's search
• [x] Thread-safe cancel methods on each of the path-trial's search
  • [x] If any of the paths fail during the ItineraryTrial, we should try to cancel all of the ongoing PathTrials. If they in fact returned canceled, then we just ignore whatever else is in the result.
  • [ ] If any of them actually succeed even if they were cancelled, then we should still treat that like a success for caching purposes.
• [x] Kicking off all of the PathTrials during an ItineraryTrial and wait for them to all complete (and cancel, if needed, as described above)
• [ ] Today, we have a config parameter that limits how many SearchSessions may be going at one time. Today, this effectively limits how many PathTrials are searching, which in turn limits how much memory the plugin can possibly use, since each of the PathTrials have a limited number of visited nodes during its A* search. This new functionality invalidates that assumption, since each SearchSession may now have multiple searches running in parallel. So, we could instead change the config parameter to something that tracks the maximum number of path algorithms running at one time (we can keep the same name, just change its description). But, we actually still have a problem: this should probably be its own ticket:
  • We can theoretically lock up all the threads on the system, blocking out all other plugins' asynchronous tasks (assuming the player's max searches config parameter is high enough). This can be fixed by instead having a maximum number of threads that can be used at a time. Since we never have multiple path trials running at once on the same thread, then this also keeps the memory usage under a maximum. So, we should do this instead.

[TheDeafCreeper]

The current new system does not process any of the PathTrials after being canceled, and I have not implemented any new stuff to do with resource limiting, mostly because I have no idea how to actually modify the config system.

Processing successful PathTrials I'll do before submitting this for review, I think I'll leave the extra config options though for a different PR.

[TheDeafCreeper]

Actually, caching doesn't seem to be done in main right now either, so I'll just open for review now.